The conventional solution for increasing high-power microwave (HPM) power is making the source bigger, including increasing the number of modules, and making antennas bigger. However, platform constraints typically make the increase of the HPM source size impractical, thereby limiting the number of elements which can be used in a given system.
More particularly, with high-power microwaves, in order to improve the amount of energy on target a number of antennas are carried on a moving platform such as an aircraft or missile in which the antennas are directional. These directional antennas provide a fixed beam so that the outgoing energy goes out only in one direction towards the target. In a typical tactical scenario, in order to place the energy on target one must physically move the antennas to point at the target or physically move the entire platform, e.g., physically move the aircraft or missile. When the platform is moving in a direction other than that which points the antenna at the target, such as in a forward direction, a sideways direction, or another direction, the platform would be required to turn back to point at the target or another direction of aim. Thus, the ability to do mission planning is limited because of the fixed positioning of the antenna, where pointing the antenna is dependent upon the orientation of the platform.
Another problem with HPM systems is the present pointing accuracy. Conventional pulsed HPM systems do not have accurate timing control and do not have an easy or straightforward solution for beam steering. For steering the beam of energy, in terms of the pulses, the use of a mechanism to locate many shots on target will provide a decent opportunity to take out the target. However, if the antennas are only pointing in one direction because they are fixed to the platform, the time at which the pulses can be turned on and off can be significantly limited.
To illustrate this principle, consider an analogy using a machine gun. If it is desirable to strafe a target with multiple shots using a fixed machine gun, it can only be done when the fixed machine gun is directly aiming at the target. Similarly, if it is desirable to strafe a target with multiple high-energy pulses, it can only be done when the vehicle with its antenna is directly aiming at the target. However, if the target is sideways with respect to the orientation of the antenna, it will be necessary to wait to maneuver the vehicle so that the vehicle-mounted antenna is pointed at the target. When the vehicle is properly aligned with the target direction, the pulses can be generated. As a result, as the vehicle passes by the target, firing can only commence once the target is immediately in the aim of the antenna.
Further, if the system aboard the vehicle is provided with the ability to dynamically point at the target as the vehicle moves by, it is possible to get more pulses on the target and therefore be more effective in taking out the target due to the buildup of the high-energy pulses. This principle assumes one can continue to shoot pulses while approaching the target or moving away from the target. In other words, shooting pulses would not be constrained to having the target positioned directly in front of the antenna.
The problem, however, is how to be able to project high-energy pulses towards a target in a steerable manner. For phased array radars, it is fairly well known that beams can be steered by adjusting the phase of the signals at an array of antennas. However, it is not at all clear how to phase ultra-short high-power pulses. Moreover, it is likewise not clear how to calculate the phase of ultra-short pulses projected by multiple antennas where there is no necessary instantaneous phase relationship between these pulses. While it is possible in conventional phased array radars to ascertain the phase relationship between continuous waves, it is not entirely clear how one could adapt phased array technology to provide beam steering for high-energy pulsed systems.
Although the concept of phased array beam steering is well developed for continuous wave low power sources, conventional pulsed HPM systems do not have accurate timing control, and thus do not have an easy or straight forward solution for beam steering. Furthermore, the possibility of constructive interference of short pulses within a wide steering angle has been thought to be questionable at best. Additionally, the idea of using a large number of very small elements stacked together in an array and to control the timing of the projection of the pulses at each of these elements to get a beam steering effect has not been possible due to the fact that, when dealing with individual pulses, it had not been proven that one could effectively time the leading edges of these pulses with highly precise phase delays to provide the appropriate beam steering characteristic.
Thus, a heretofore unaddressed need exists in the industry to address the aforementioned deficiencies and inadequacies.